Human Anatomy and Physiology : IV. Respiratory System

The lungs are the primary organs for respiration in mammals and most other vertebrates. In mammals, two lungs are located near the backbone on either side of the heart. Its function in the respiratory system is to extract oxygen from the atmosphere and transfer it into the bloodstream and to release carbon dioxide from the bloodstream into the atmosphere, in a process of gas exchange.

The action or process of inhaling and exhaling of air is known as respiration. It is a metabolic process, common to all living things. During the expiration, nitrogen comes out with the same amount as it was entered during the inspiration, while the percentage of oxygen is decreased and amounts of carbon dioxide and water vapour are increased in expired (exhaled) air.

Getting oxygen to the body's cells requires three major events:

• Uptaking oxygen from the air to the lungs;
• Transporting that oxygen in the blood;
• Delivering the oxygen to cells and tissues throughout the body.

The function of the respiratory system is to move two gases: oxygen and carbon dioxide. Gas exchange takes place in the millions of alveoli in the lungs and the capillaries that envelop them. In this process, inhaled oxygen moves from the alveoli to the blood in the capillaries, and carbon dioxide moves from the blood in the capillaries to the air in the alveoli.

Hypoxemia or low level of oxygen in the blood describes a lower than normal level of oxygen in the blood. In order to function properly, our body needs a certain level of oxygen circulating in the blood to cells and tissues. When this level of oxygen falls below a certain amount, hypoxemia occurs and you may experience shortness of breath. In other words, when there is a decrease in the concentration of oxygen in the blood, the rate of breathing increases.

Carbon monoxide mainly causes adverse effects in humans by combining with haemoglobin to form carboxyhaemoglobin (HbCO) in the blood. This prevents haemoglobin from carrying oxygen to the tissues, effectively reducing the oxygen-carrying capacity of the blood, leading to hypoxia. Additionally, myoglobin and mitochondrial cytochrome oxidase are thought to be adversely affected. Carboxyhaemoglobin can revert to haemoglobin, but the recovery takes time because the HbCO complex is fairly stable.

Adenosine triphosphate (ATP) is the high energy molecule that stores the energy. The conversion of ATP to ADP is an extremely crucial reaction for the supplying of energy for life processes. ATP hydrolysis is the final link between the energy derived from food or sunlight and useful work such as muscle contraction, the establishment of electrochemical gradients across the membrane and biosynthetic processes necessary to maintain life.

ATP + H₂O → ADP + Pi + energy

Respiration is a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into Adenosine Triphosphate (ATP), and release waste products.

Aerobic respiration is the release of energy from glucose or another organic substrate in the presence of oxygen, resultant glucose is converted into CO₂ and H₂O. By this process, large amount of energy is released. Aerobic respiration happens all the time in the cells of animals and plants.

In the process of cellular respiration, glucose breaks down into pyruvate through glycolysis in cytoplasm. Pyruvate (CH₃COCOO⁻) has three carbon molecules. In presence of oxygen (in aerobic respiration) pyruvate produces carbon dioxide and water, along with the generation of energy. Due to lack of oxygen, pyruvate gets converted to lactic acid in the muscles. In absence of oxygen (in anaerobic respiration), pyruvate gets converted to carbon dioxide and ethyl alcohol (ethanol).